The present invention relates to a screen for projection.
FIG. 2 shows the structure of a conventional screen for projection. This screen for projection is composed of combination of a Fresnel lens 4 and a lenticular lens 5.
As shown in FIG. 2, the Fresnel lens 4 serves to convert rays from a light source 1 into parallel rays which are substantially perpendicularly incident upon the lenticular lens 5. On the other hand, the lenticular lens serves to scatter the rays from the Fresnel lens 4 with sufficient control.
In conventional lenticular lenses and Fresnel lenses, there can be used transparent thermoplastic resins such as acrylic resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, etc. Of these, the acrylic resins are often used by taking advantages of their transparency, hardness, durability and workability.
In the lenticular lenses, there are widely used materials having light-diffusion properties which are obtained by mixing the above-mentioned thermoplastic resins with light-diffusing substances such as silica, alumina, clay, glass, beads, etc.
In a screen for projection, both light-diffusing capability and light-transmitting capability are important. Conventional screens for projection have satisfactory light-diffusing properties but are disadvantageous in that they have a low total light transmittance, resulting in a dark image plane of screen. When the total light transmittance is increased for brightening the image plane of screen, the light-diffusing properties are deteriorated, so that the range of visual field is narrowed. Thus, it has been difficult to satisfy both of the above requirements at the same time.
Moreover, the conventional screens for projection are disadvantageous in that a moire pattern due to the pitches of a Fresnel lens and a lenticular lens tends to be formed on the image plane of the screen. Particularly when a light source for projection is not CRT but a liquid crystal, a moire pattern due to the pitch of picture element of the liquid crystal is formed and this is a problem.